As known, power adapters or power supplies are essential for many portable electronic devices such as laptop computers, notebook computers, tablet computers, communication products or network products. As shown in FIG. 1, a power adapter 1 is interconnected between a power source (e.g. a utility power source) and a portable electronic device 2 (e.g. a notebook computer) and configured to receive utility power and convert the utility power into a DC voltage required for powering the portable electronic device 2. The power adapter 1 principally includes an AC/DC power converter 10, a first power cord set 11 and a second power cord set 12. The first power cord set 11 includes a first electrical connector 111 and a first power cord 112. The first electrical connector 111 is detachably connected to a mating electrical connector 21 of the portable electronic device 2. The second power cord set 12 includes a second electrical connector 121 and a second power cord 122. The second electrical connector 121 is detachably connected to the utility power source. The second power cord set 12 is used to receive the utility power and delivery the utility power to the AC/DC power converter 10. By employing the AC/DC power converter 10, the utility power is converted into a DC voltage and the DC voltage is delivered to the portable electronic device 2 via the first power cord set 11 and the mating electrical connector 21 so as to power the portable electronic device 2.
Recently, low power loss and high efficiency are becoming basic requirements for power adapters or power supplies. However, when the conventional power adapter is plugged into a wall power source but not physically connected to a DC-powered electronic device, or when the conventional power adapter is plugged into a wall power source but is coupled to a DC-powered electronic device that is not drawing current, the conventional power adapter remains on and consumes energy. To minimize wasted energy under such operation conditions, U.S. Pat. No. 7,911,817 has disclosed systems and methods for controlling energy consumption of power adapters, as shown in FIG. 2. The power adapter is provided with an auto-sensing capability to sense when no DC load is present at the output of the power adapter by monitoring for absence of load-indicative signals communicated to the power adapter from a coupled DC-powered electronic device. Such an absence of load-indicative signals indicates that the power adapter is not connected to DC-powered electronic device, or that a connected DC-powered electronic device is inactive (i.e. drawing no power). Upon detection of such a no load condition, the power adapter enters a no load mode during which the power adapter output is turned off in order to reduce energy consumption by the power adapter, and only produces short recurring voltage pulses (hiccups) at the power adapter output. Upon detection of load-indicative signals communicated to the power adapter from a coupled DC-powered electronic device, the power adapter output enters a normal mode and provides its normal regulated power value to the power adapter output for powering the coupled DC-powered electronic device.
However, the load-indicative signal pin or the wire of the power adapter may be broken after a long time usage or an abnormal plug action between the electrical connector of the power adapter and the mating electrical connector of the DC-powered electronic device. If the load-indicative signal pin or the wire of the power adapter is broken, the power adapter will always regard that the power adapter is unplugged with the DC-powered electronic device so that the power adapter will always be operated in hiccup mode, which can't power the DC-powered electronic device normally.